Phase shifting circuit



Oct. 19, 1948. s, BERKOFF 2,451,796

PHASE SHIFTINGCIRGUIT Filed Sept. 23, 1945 FigJ.

Inventor: SCBTTIOUT' BeTkoff,

by WW5.

H is Attorney.

than 180 degrees.

Patented Oct. 19, i948 PHASE SHIFTING CIRCUIT Seymour, Berkofi,Bridgeport, Conn., assignor to General Electric Company, a corporationof New York Application September 23, 1943, Serial No. 503,545

6 Claims. (Cl. 323-119) My invention relates to electric circuits and,more particularly, to electric circuits for shifting the phase of thealternating potential derived i'rom the source with respect to thepotential of that source. It is an object of my invention to provide anew and improved electric phase shifting circuit.

It is another object of my invention to provide a new and improved phaseshifting circuit in which the output voltage may be varied through 360electrical degrees relative to the input voltage with substantiallysmall change in relative magnitudes.

It is a further object of my invention to provide an improved electricphase shifting circuit which is simple in assembly and operation and thecomponent elements of which are standard electrical circuit elements andwhich may be replaced in use with relatively little difllculty.

While my invention is of general application in electric control orregulating circuits, it is particularly adapted to use in connectionwith the sweep circuit of a cathode ray tube. In such applications,particularly when used in pulse signalling systems, it is desirable tocontrol the starting time of a trace so that a selected image appears atthe beginning of a trace and facilitates comparison of other images. Inorder that this result be obtained, it is essential that the phaseshifting device have a range of substantially 360 electrical degrees.

Accordingly, it is another object of my invention to provide a new andimproved means for shifting the phase of a sine wave over a rangegreater than 360 degrees and which requires only a combination ofresistors, condensers, and electron discharge tubes.

One of the features of my invention is the employment of an electronicdischarge tube as a phase splitter in a phase shifting circuit to avoidthe necessity of employing transformers and the use of the combinationof capacitances and resistances in the output circuit of the electronicdischarge device to obtain a phase shift of more In another of itsaspects, my invention employs two electronic discharge devices havingsimilar output circuits and connected serially to obtain a phase shiftof more than 360 electrical degrees.

The features of my invention which are be- .lieved to be novel are setforth with particularity reference to the following description taken inconnection with the accompanying drawing in which Fig. 1diagrammatically illustrates an embodiment of my invention in which thephase shifting circuit illustrated provides an adjustablephase shift ofmore than 180 electrical degrees; Fig. 2 is a vector diagramillustrating certain voltage and current relationships in the phaseshifting circuit of Fig. 1; and Fig. 3 is a modification of the circuitof Fig. 1 and illustrates a circuit capable of producing a phase shiftof more than 360 electrical degrees.

In Fig. 1 there is shown a source of alternating voltage I and apparatusfor producing an alternating voltage variable in phase relative to thephase of this source and of fairly constant magnitude and comprising theelectronic discharge device 2 having an output circuit which includesthe output terminals 3 across which a suitable load circuit, such as thesweep circuit of a cathode ray tube, may be connected.

'The electronic discharge device 2 comprises an anode 4, a controlelectrode 5, and a cathode 5, the cathode 8 being connected to groundthrough a cathode resistance I. The source of alternating voltage I isconnected between control electrode 5 and ground. Operating potentialfor the anode 4 may be supplied from any suitable source, such as thebattery 8, through an anode load resistance 9. In the portion of thecircuit thus far described, the cathode resistance I and the anoderesistance 9 have substantially equal ohmic values so that theelectronic discharge device 2 operates as a phase splitting means andproduces voltages across the resistances I and 9 which are equal andapproximately 180 degrees out of phase.

In order to provide means for shifting the phase of the voltageimpressed across the output terminals 3 with respect to the phase of thealternating voltage source I, a phase shifting resistance II isconnected between anode l and cathode 6, this resistance having amovable contact l2. A capacitance i3 is connected between the anode 4and the movable contact 12. Likewise, the upper terminal of the pair ofoutput terminals 3 is connected to the juncture of capacitance l3 andcontact l2. When the portion of the phase shifting circuit comprisingresistance Ii and capacitance I3 is combined with device 2 and its loadresistances, as the movable contact I: is moved along resistance [I fromits upper to its lower terminal, a phase shift of substantially 180degrees in the voltage impressed across the output terminals 3 isobtained. In order to increase this shifting of the phase of outputvoltage of the circuit to a value of greater than 180 electricaldegrees, I provide a capacitance I4 connected between anode 4 andground.

Operation of the circuit of Fig. 1 to produce a phase shift of more than180 electrical degrees may best be explained by reference to the vectordiagram shown in Fig.2. To assist in explaining the voltage-currentrelationships in the circult, the anode 4 has been designated as thepoint P, the cathode 6 as the point C, the grid 5 as point G, and groundas the point 0. In Fig. 2, therefore, the vector Ecp denotes thepotential rise between cathode 6 and anode 4. It is assumed that theresistance II is a very large resistance so that a negligible amount ofcurrent passes therethrough when the movable contact I2 is at the anodeend of resistance II and condenser I3 is short-circuited. The circuitbehavior is then the same as though these elements, the resistance I Iand capacitance I3, were not present. The alternating currentanode-toground voltage rise, Eop, in terms of the input voltage E03, isgiven by the equation 'I- vr( EL j E p+#R+Rm.)j n In this equation andthose which follow hereinafter, the designation of the circuit elementsis as follows:

R =internal plate resistance of tube 2 Rc=cathode load resistance 1Rat=equivalent plate load resistance,

On the other hand when the contact point I 2 is at the cathode end ofresistance II, capacitance I 3 is effectively connected between theplate 4 and cathode 6. If we consider resistance I I to be of a verylarge value, the alternating current cathodeto-ground voltage rise E00is then In Equation 2 it will be seen that E00 may either lead or lagEog, depending on the sign of the 7 term in the denominator. If Xnr, issufficiently large (reactance of capacitor I4 is sufficiently small)compared to REL, the sign of the 7' term will be negative, and Eoc willthen lead E0 which condition is shown in the vector diagram of Fig. 2.

Also, from Equation 1, it may be seen that Eop must lag the vector Eog.whatever the value of XEL. This follows because the denominator ofEquation 1 has a greater resistance component than the numerator, whilecontaining the same reactance component.

If X121. is large enough to cause Eoc to lead E03, the vector relationsare then as shown in Fig. 2. The anode-to-cathode voltage rise Ecp isapplied 4 across the circuit comprising resistance II and capacitance I3in which the phase is adjustable by varying the position of contact I2.A net current I, having a phase angle which leads the voltage Ecp, flowsthrough the circuit comprising resistance II and capacitance I3.

Since Ecp is applied across this circuit, the current I may be varied inphase with Ecp when contact I2 is at the upper terminal of resistance IIand the capacitance I3 is short-circuited to a condition where it leadsthe voltage Esp by degrees, which condition occurs when contact I2 is atthe cathode terminal of resistance II. The locus of the potential ofpoint D at the junction of capacitance I3 and contact I2 variesapproximately along the arc of a semicircle having the voltage Ecp asits diameter. It should be noted that the resistance of the portion ofpotentiometer II which is across the capacitor I3 is large compared withthe reactance of capacitor I3, and causes but small deviation from atrue circle diagram. The output for each of the systems impressed acrossoutput terminals 3 is be tween ground and the point D, ground beingdenoted by the common point 0 of the vectors Eop and E00 in the vectordiagram of Fig. 2. From the diagram, therefore, it is seen that thephase position of the vector Eon, the voltage across the outputterminals 3, may be varied over a range greater than degrees. Thevariation in amplitude of the voltage Eop, of course, depends upon thephase angle between the voltages Eoc and E011. When this angle is 180degrees, the amplitude of the output voltage remains substantiallyconstant. This phase angle between E00 and Eop is determined by thevalue of the capacitance I4 which controls the value of the quantity XELin the equations given above. The value of this capacitance need be onlysuflicient to make the angle between Eoc and Eop equal to 180 degrees,which value may be found by equating the resistive and reactive terms inEquations 1 and 2. Any value of XEL greater than this will allow thecircuit to provide a phase shift considerably greater than 180 degrees;in fact, phase shifts up to slightly less than 270 degrees may beobtained. Of course, the amplitude variation increases as the obtainablephase shift increases over 180 degrees.

In the foregoing discussion, the vector diagram of Fig. 2 holds only fora given frequency. However, it may be seen by a study of Equations 1 and2 that the total obtainable phase shift remains approximately constantover a large range of frequencies, since E00 and Eop maintainpractically a constant phase position with respect to E0; as thefrequency is varied. Thus the circuit is not limited to use at a singlefrequency.

In Fig. 3, I have shown a modification of my phase shift circuit inwhich a variation of greater than 360 electrical degrees may be obtainedbetween the voltage source I and the voltage across any small loadimpressed across output terminals 3. In this modification of the phaseshifting cir-' cuit, a pair of electronic discharge devices 2, 2' havecircuit elements corresponding to the elements used in the circuit ofFig. 1 connected thereacross, In Fig. 3 impedance elements, associatedwith electronic discharge device 2 and corresponding to impedanceelements shown in Fig. 1, are designated by similar characters, whilecorres nding impedance elements associated with electronic dischargedevice 2 are designated by similar numerals differentiated by priming.

The source of alternating voltage I, is connected between ground andcontrol electrode Ii through a coupling capacitor and a voltage dividinresistance 2|. The use of resistor 2| is not necessary in allapplications and this resistor may be omitted when the source ofalternating voltage I does not swing the tube grid beyond class Aoperation, i. e., cause the tube 2 to be cut off during any portion of acycle. A cathode bias resistor 22 is connected between cathode 6 andcathode load resistance 1 and a grid leak resistance 23 is connectedbetween controlielectrode 5 and the common point of resistances 22 andI. The phase shifting potentiometer l l is connected between anode l andthe common point of cathode resistances 22 and The movable contact I2 isconnected to the control electrode 5' of electronic discharge device 2'through a coupling capacitance 25, The output terminals 3' of the phaseshifting circuit are connected respectively to ground and the movablecontact l2 on phase shifting potentiometer l I. In applications wheredesired. the contacts l2, l2 may be mechanically linked for unicontroloperation. When so connected, as the contacts l2 and I2 are moved fromthe anode terminals of their associated resistances to the cathodeterminals thereof, the

voltage impressed across output terminal 5 is shifted with respect tothe input voltage I through an angle greater than 360 electricaldegrees, the exact angle of the phase shift being determined by thevalues ofcapacitances H, I 4' according to the considerations pointedout in connection with the discussions of the circuit of Fig. 1 and thevector diagram of Fig. 2.

By way of illustration only and not in any sense by way of limitation,the following representative values are those whichhave been foundsuitable in a particular phase shifting receiver embodying my inventionand constructed according to the circuit of Fig. 3. In this receiver atype GSN'TGT tube was employed in the dual capacity of the dischargedevices 2, 2". The values of the impedance elements used are as follows:

Load resistances I, I, 9, 9 ohms 22,000 Potentiometers II, II megohms 2Capacitances ll, ll,

l3, I3 micromicrofarads 3,300

I The frequency of the input of the source of alternating voltage was ofthe range of 300to 600 cycles, and it was found that with the circuitelements given above, the amplitude of the output voltage and range ofobtainable phase shift remained substantially constant over thisfrequency range. A phase shift of considerably more than 360 degrees wasobtained, As the phase controls were rotated, the amplitude of theoutput varied about In applications where this amplitude variation isobjectionable, capacitors l4 and H may be reduced in size to give only360 degrees phase shift, in which case the amplitude variations withphase shift will be reduced to about 5%.

From the foregoing. it may be seen that my invention provides animproved phase shift circuit which may be employed to obtain shiftsbeages through a range of greater than 360 electrical degrees, a rangeparticularly desirable for use in conjunction with sweep circuits ofcathode ray tubes. The component elements of my phase shifting circuitare readily available and easily assembled and require no transformerconnections with tap adjustments.

While I have shown a particular embodiment of my invention, it will ofcourse be understood that I do not wish to be limited thereto sincevarious modifications may be made. and I contemplate by the appendedclaims to cover any such modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent inthe UnitedStates is:

1. In a phase shift network, an electron discharge device having ananode, control electrode, and a cathode, a source of operating voltagehaving its positive terminal connected to said anode through aresistance and its negative terminal connected to said cathode through aresistance, means to supply an alternating voltage between said controlelectrode and cathode, a resistance connected between said anode andcathode, and

a load circuit connected between said negative terminal and a pointvariable along said last resistance in accordance with the phase shiftdesired.

2. In a phase shift network, an electrondischarge device having ananode, control electrode, and a cathode, a source of operating voltagehaving its positive terminal connected to said anode through aresistanceand its negative terminal connected to said cathode through aresistance, a source of alternating voltage connected between saidcontrol electrode and said cathode, a resistance connected between saidanode and cathode, a load circuit connected between said negativeterminal and a point variable along said last resistance in accordancewith the phase shift desired, and means to increase said phase shift toa value in excess of 180 degrees as said point is moved from one end ofsaid last resistance to the other.

3. In a phase shift network, an electron discharge device having ananode, control electrode, and a cathode, a source of operating voltagehaving its positive terminal connected to said anode through aresistance and its negative terminal connected to said cathode through aresistance,

means to supply an alternating voltage between said control electrodeand cathode, a resistance connected between said anode and cathode, areactance connected between said anode and said negative terminal, and aload circuit connected between said negative terminal and a pointvariable along said last resistance in accordance control electrode andcathode, a source of opertween the phases of incoming and outgoingvoltating voltage having opposite terminals connected to said anode andcathode through respective resistances, a capacitance connected betweensaid anode and the negative terminal of said source of operatingvoltage, a resistance connected between said anode and said cathode, asecond capacitance connected between said anode and a movable contact onsaid last resistance, and an output circuit connected between saidmovable contact and said negative terminal, said capacitances havingsuch values relative to said resistances that movement of said contactalong said second resistance is effective to shift the phase of thealternating voltage impressed across said output circuit through anangle greater than 180 electrical degrees.

5. In combination, a source of alternating voltage, apparatus forproducing an alternating voltage variable in phase relative to thevoltage of said source and of substantially constant magnitude andcomprising means connected to said source for producing equal andopposite voltages with respect to a point of fixed potential, said meansincluding a pair of terminals, a resistance connected across saidterminals and including a movable contact, a first reactance connectedbetween said movable contact and one of said terminals, a secondreactance connected between said one terminal and said point, and anoutput circuit connected between said movable contact and said point,said second reactance having such a value that the phase variationproduced in said output circuit as said contact is moved between theterminals of said resistances is at least 180 degrees.

6. In combination, a source of alternating voltage, apparatus forproducing an alternating voltage variable in phase relative to thevoltage of said source and comprising a pair of electron dischargedevices each having an anode, a cathode, and a control electrode, asource of operating voltage having its positive terminal connected tosaid anodes through resistances and its negative terminal connected tosaid cathodes through resistances, each of said devices having aresistance and a capacitance connected between the anode thereof andground, each of said last resistances having movable contacts thereon,means connecting said source of alternating voltage between the controlelectrode of one of said devices and ground, means connecting thecontrol electrode of the other of said devices to the movable contactassociated with said one device, and output terminals connected betweenthe other of said movable contacts and ground, said capacitances havingsuch values that movement of said contacts along said resistances isefiective to shift the phase of the alternating voltage impressed acrosssaid output terminals through an angle of at least 360 electricaldegrees.

- SEYMOUR BERKOFF.

REFERENCES CITED The following references are oi. record in the file ofthis patent:

UNITED STATES PATENTS

